Pentavalent refers to a chemical species that has a valency of five, meaning it can form five bonds with other atoms. This term is often used in the context of certain elements, such as phosphorus or vanadium, which can exhibit this valency in various compounds. Pentavalent compounds play significant roles in chemistry, particularly in the formation of complex molecules. In the field of immunization, the term "pentavalent vaccine" is used to describe a vaccine that protects against five different diseases. For example, the pentavalent vaccine for children typically includes protection against diphtheria, tetanus, pertussis, hepatitis B, and Haemophilus influenzae type b. This combination helps streamline immunization efforts by reducing the number of shots needed.